"It wasn't the one that had killed the woman, says Graeme Shannon, a behavioral ecologist at Colorado State University, in Fort Collins. "It was just the first elephant they encountered—a young bull on the edge of a swamp."

The Maasai spiked him with spears and, their anger spent, returned home. Later, the animal died from his wounds.

Elephants experience those kinds of killings sporadically. Yet the attacks happen often enough that the tuskers have learned that the Maasai—and Maasai men in particular—are dangerous.

The elephants in the Amboseli region are so aware of this that they can even distinguish between Ma, the language of the Maasai, and other languages, says a team of researchers, who report their findings today in the Proceedings of the National Academy of Sciences.

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A Maasai herder leads his cattle to drink at the edge of a swamp in the Amboseli National Park in Kenya.

Photograph by Graeme Shannon

Powers of Discrimination

The results add to "our growing knowledge of the discriminatory abilities of the elephant mind, and how elephants make decisions and see their world," says Joyce Poole, an elephant expert with ElephantVoices in Masai Mara, Kenya.

Indeed, previous studies have shown that the Amboseli elephants can tell the cattle-herding, red-robed Maasai apart from their agricultural and more blandly dressed neighbors, the Kamba people, simply by scent and the color of their dress.

The elephants know too that walking through villages on weekends is dangerous, as is crop raiding during the full moon.

They're equally aware of their other key predator, lions, and from their roars, know how many lions are in a pride and if a male lion (the bigger threat because he can bring down an elephant calf) is present.

And they know exactly how to respond to lions roaring nearby: run them off with a charge.

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A group of elephants defensively bunch together, with the matriarch of the family at the front.

Photograph by Graeme Shannon

Flight or Fight

Intriguingly, when the Amboseli elephants encounter a red cloth, such as those worn by the Maasai, they also react aggressively. But they employ a different tactic when they catch the scent of a Maasai man: They run away. Smelling the scent of a Kamba man, however, troubles them far less.

"They have very clear behavioral responses in all of these situations," says Karen McComb, a behavioral ecologist at the University of Sussex, in the United Kingdom. "We wondered if they would react differently to different human voices."

To find out, she and her colleagues played recordings to elephant families of Maasai and Kamba men, as well as Maasai women and boys, speaking a simple phrase in their language: "Look, look over there, a group of elephants is coming."

Over a two-year period, they carried out 142 such playbacks with 47 elephant families, each time playing a different human voice through a concealed speaker placed 50 meters (164 feet) from the animals. They video-recorded the elephants' reactions to the various human voices, including a Maasai man's voice they altered to sound like a woman's.

Watch elephants retreat from a perceived threat:

As soon as an elephant family heard an adult Maasai man speak, the matriarch didn't hesitate, the researchers say. "She instantly retreats," Shannon says. "But it's a silent retreat. They sometimes make a low rumble, and may smell for him, too, but they're already leaving, and bunching up into a defensive formation. It's a very different response to when they hear lions."

In contrast, the voices of Kamba men didn't cause nearly as strong a defensive reaction: The elephants didn't consider the Kamba a serious threat.

"That subtle discrimination is easy for us to do, but then we speak human language," says Richard Byrne, a cognitive biologist at the University of St. Andrews, in Scotland. "It's interesting that elephants can also detect the characteristic differences between the languages."

Fear Men, Not Boys (or Women)

The Amboseli elephants were also sufficiently tuned in to the Maasai language that they could tell women's and boys' voices from men's, seldom turning tail in response. "Maasai women and boys don't kill elephants," Shannon points out. Nor were the elephants tricked by the man's altered voice; when they heard it, they left at once.

"The elephants' decision-making is very precise," McComb says, "and it illustrates how they've adapted where they can to coexist with us. They'd rather run away than tangle with a human predator."

"Unfortunately, there are going to be things they cannot adapt to, things such as humans' ability to come after them with automatic weapons or mass poisonings," McComb says. "And in those situations, we have to protect them—or we will lose them, ultimately."